Chromatography is generally used for the analysis or separation and refinement of various substances. Liquid chromatography is divided largely into adsorption chromatography and partition chromatography according to the separation mechanism.
Partition chromatography is further divided into normal-phase partition chromatography and reversed-phase partition chromatography according to the polarities of the elute and the packing material.
Most of the packing materials used for adsorption chromatography and normal-phase partition chromatography are totally porous silica gel packing materials in which macropores and micropores are dispersed reticulately. Alternatively, inorganic supports such as alumina and porous glass materials, and porous polymers such as polystyrene-divinyl benzene, polyvinyl alcohol and polyhydroxy methacrylate are used. Calcium hydroxide powder, calcium phosphate gel, etc. are also used for specific purposes.
Above-described chromatographic supports (e.g., silica gel) modified with alkyl groups, such as octadecyl groups, are often used for reversed-phase chromatography.
Other packing materials are also used, for example, packing materials for cation-exchange liquid chromatography such as silica gel or a porous polymer with a compound having a sulfonyl group or carboxyl group combined therewith and packing materials for anion-exchange liquid chromatography such as silica gel or a porous golymer with a quaternary ammonium or a diethylamino group combined therewith.
All of these packing materials, however, suffer from various problems. Especially, the discrimination between saturation and unsaturation is so poor that the discrimination between substances having similar molecular weights is very difficult. An improvement at this point has therefore been in strong demand.
As a packing material for meeting such a demand, the present invention developed a packing material disclosed in Japanese Patent Laid-Open No. 199155/1989.
This packing material is a swelling clay mineral with the ions between layers substantially replaced by cations other than sodium ions, especially, silver ions. Since this packing material has discrimination between saturation and unsaturation, it is possible to separate a wide variety of unsaturated compounds into substances according to the degree of unsaturation. The packing material is therefore used as a means of analyzing and separating various compounds.
Even this packing material composed of the clay mineral, however, very strongly adsorbs a highly unsaturated compound having a degree of unsaturation of not less than 3, and the peak in chromatography becomes broad, which makes efficient and short-time analysis and separation impossible.
In addition, a poor reproducibility of retention time in certain solvents has been a big problem.